Italian researchers have made a new discovery that solidifies the understand that homosexuality — at least in men — has a strong genetic component. Though this study does not identify a specific gay gene, which probably does not exist, it does demonstrate what role genetics play.

Andrea Camperio Ciani at the University of Padova discovered that the mothers and maternal aunts of gay men tend to have significantly more offspring than those of straight men. Tthere seems to be at least one gene on the X chromosome that creates a trade-off in men and women. The men turn out gay (and hypothetically less likely to reproduce), but the women’s fecundity increases, making them more likely to have more offspring. In a sense, the gene makes men more attracted to men, but the women more attractive to men. Not only are they more fertile and have less complications during pregnancy, but these women are also more extroverted and have few family problems and social anxieties.

This is called the “balancing selection hypothesis,” and it effectively demonstrates how male homosexuality — as documented not only in humans but hundreds of species — does not actually contradict expectations that evolution favors reproduction. Still, homosexuality is clearly not determined by a single factor. Studies have shown, for example, that exposure to certain levels of hormones in the womb can play a role in sexuality. Twin studies also suggest other genetic components, even in women. But this research may help explain why female sexuality tends to be more fluid while men’s tends to be more fixed; this “trade-off” gene may just not be playing the same role.

Scientists may never fully identity what complex combination of factors determines sexuality, but there is still plenty of evidence to conclude that it is natural and healthy part of human diversity. With each new discovery about the nature of homosexuality, discrimination against people for being gay becomes more repugnantly indefensible.